Many processes result in the formation of streams containing acetic acid and acetic anhydride. Carbonylation processes are an example. Carbonylation coproduction technologies exist in which both methanol and methyl acetate are carbonylated together to produce a product mixture of acetic acid and acetic anhydride. Some examples are described in European Patent Application having a Publication No. EP0087869. Some methyl acetate carbonylation processes use acetic acid as a solvent, so that the product stream contains both the acetic anhydride product and the acetic acid solvent. Furthermore, some acetic anhydride manufacturing processes include steps in which a portion of the acetic anhydride product is reacted with methanol to produce acetic acid (along with methyl acetate) such as described in U.S. Pat. No. 7,737,298 and U.S. Patent Application having Publication No. 2012/0123156. Such processes allow alteration of the relative amounts of acetic acid and acetic anhydride in the resulting stream. Streams may also be partially hydrolyzed with water to convert some of the acetic anhydride to acetic acid.
Acetic anhydride and acetic acid products are often separated and purified for sale or use in subsequent reactions. It may also be advantageous in some cases to combine acetic acid products containing small amounts of acetic anhydride with water to hydrolyze the acetic anhydride and thus produce an aqueous acetic acid solution. The separation and purification of two product streams results in capital and operating expense associated with two lines of equipment. It would be advantageous to identify ways to reduce such costs.